When Jesus appeared to the Nephites, he told them that they were among the “other sheep” that must be brought into the fold (3 Nephi 15:21). 1 Nephi 5:14 states that Lehi was a descendant of Joseph, and in Alma 10:3, Amulek tells the people of Ammonihah that Lehi was a descendant of Manasseh. The tribes of Ephraim and Manasseh, sons of Joseph, were among the northern tribes that became “lost.” The Nephites, then, were actually part of the “lost” tribes, and the “other sheep” referred to them, among others. However, the people of ancient Judea understood him “not, for they supposed it had been the Gentiles; for they understood not that the Gentiles should be converted through their preaching” (3 Nephi 15:22). And, just as Jesus Christ remembered these “other sheep,” he will remember all of God’s children, today and forever.
Book of Mormon Central, “Why Did Jesus Say That There Were “Other Sheep” Who Would Hear His Voice? (3 Nephi 15:21), KnoWhy 207 (October 12, 2016).